<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
    <style>
        #container div{
            width: 100%;
            height: 100%;
            border: 1px solid red;
        }
        #container{
            display: flex;
            /*弹性布局默认显示按行row*/
            flex-direction: row;
            /*默认从头（起点）flex-start排列，space-between:两端对齐，space-around平均间隔*/
            justify-content: space-around;
          /*  cursor: text;*//*设置鼠标样式*/
        }
        #fixed{
            width: 20px;
            height: 20px;
            border: 1px solid red;
            position: fixed;/*窗口定位，相对窗口的位置不会随滚动条等东西而变化*/
            left: 500px;
        }
    </style>
</head>
<body>
    <div id="fixed"></div>

    <div id="container">
        <div>1</div>
        <div>2</div>
        <div>3</div>
    </div>

</body>
</html>